Acoustic diaphragm



Feb. 7, 1933. c. F. DILKs ACOUSTIC DIAPHRAGM YFiled Oct. 7, 1950 2 Sheets-Sheet l IIIJIII INVENTOR.

'ATTORNEY Feb. 7, 1933. c. F. DILKs I 1,896,073

ACOUSTIC. DIAPHRAGM Filed Oct. 7, 1930 2 Sheets-Sheet 2 INVENTOR FDHks Patented Feb. 7, 1933 UNITED STATES PATENT OFFICE ACOUSTIC DIAPHRAGM Application led October 7, 1930. Serial No. 486,989.

My invention relates to acoustic diaphragms of the general class including cone or other diaphragms of relatively large area employed in radio, public address sound reproducers, and the like.

Principal objects and advantages ofthe invention are:

To provide a diaphragm which gives exceptionally faithful sound and tone reproduction with capability of large volume or sound intensity in proportion to its area when the input energy 1s adjusted for such large volume, withoutundesirable tone distortions including those of the character usually called blasting, and effect equally faithful reproduction in lower ranges of volume; to so construct or arrange the diaphragm that different of its portions or zones respond most readily to different ranges of sound frequencies or frequency;

and also to in effect damp or reduce the relative intensity of frequencies of certain ranges, such for example, as those corresponding to the undesired or discordant sixth harmonic.

A further object is to realize these and other objects or advantages in a diaphragm composed of inexpensive material which is at the same time of a character which has a low inherent,resonance but is readily respon sive to applied vibrations and produces high acoustic pressure in proportion to input energ 'lo realize the stated and other purposes and advantages, diaphragme embodying the invention consist, as briefly described, of a plurality of lamina: or sheets, or at least certain zones or areas include a plurality of lamin, such layers or laminations consist- 40 ing preferably of material of a generally fibrous character such as, in a preferred example, paper of relatively soft composition or texture and of irregular or crepe-like formation, having relatively rough or crinkly surfaces. A good example of a preferred material available for this purpose is paper of the character used for paper towels. In Iorder to provide sufficient structural strength and stiffness throughout, the diaphragm j neferably includes throughout its area at least two or more layers of the sheet material, and these layers or laminas are se cured together by a suitable adhesive of which tapioca paste is mentioned as a preferred ingredient, for reasons stated hereto include and relatively damp intermediate audio-frequencies and the undesired sixth harmonic.

'lhe stated thickness variation also provides for faithful reproduction of tones of different frequency anges with proper relative intensities. Thus, in one preferred embodiment of my invention, l provide a relatively wide zone extending' outward from the apex, of minimum thickness, which has a natural vibration frequency corresponding to the high audio-frequencies; the intermediate thickened Zone has a natural frequency corresponding to intermediate audio-frequencies, and the peripheral thickened zone res onds naturally to the lower frequencies'veo wit lout rattling', blasting, or hollow tone. effects.

As otherwise stated, the diaphragm, which is thrown into loop or segment and node formations corresponding to vibratory movements of a musical string, and extending in all directions, axially as well as circumferentially of the diaphragm, has its thickness in different zones so proportioned that each zone favors or tends to increase the amplitude of the loops or segments corresponding to a certain frequency range and the intermediate thickened zone includes the nodal points correslwnding to the undesired sixth harmonic with resulting substantial suppression of that harmonic and elimination of discordant effects produced by it.

The tone quality is further improved in some cases by applying and securing by adhesive a controlling or dannvnng ring in the 50 j clples of constructlon or' arrangement may nature of a heavy cord, located relatively near the periphery of the cone or adjacent theJ inward edge of the peripheral thickened zone. The central portion or apex of the cone may be shaped or conformed in various ways for connection to driving` elements of different character, as sufliciently explained below.

Desirably the periphery-of the diaphragm or cone is connected to and yieldably supported on an apertured sound board or other suitable support by annular strips of suitable iiexible material, such as leather.

The various paper pieces composing the diaphragm maybe shaped in various ways to conveniently provide the multiple layers and to build up the relatively thickened zones, as also sufficiently explained in detail below.

The characteristics and advantages of the invention are further sufficiently explained in connection with the following detail description of the accompanying drawings, which show representative embodiments. After considering these examples, skilled persons will understand that many variations may be made without departing from the principles disclosed, and I contemplate the employment of any and all structures that are properly Within the scope of the appended claims; A

Fig. 1 is an elevation, either front or rear, depending on its positionI in use, of a diaphragm embodying the invention in one form. y

Fig. 2 is a side elevation.

Fig. 3 is a pla of one form of a paper sheet employed in building up the main diaphragm l structure.

Y enlarged.

.Figa 4 and 5 show other, forms of paper pieces use d in the thickened zones.V

F1g.6 1s an axial section of Figs. 1 or 2,

Fig. 7 is a sectional detail of a portion of the diaphragm wall, showing particularly 1n somewhat exaggerated manner for the sake of clearance, the rough or crepe-like paper preferably employed as the cone vbody material While I have here illustrated only diapliragms of conical forms and such forms are preferred'iny some cases, the presented prinalsobe applied toiat diaphragms.

As above stated-the preferred material for this purpose is paperof relatively soft and rough texture, such as paper toweling, and

in order to provide sufficient mechanical strength and stability the diaphragm wall at all points preferably includes a plurality, or as shown, three layers, 10, of this material. It is impracticable to show the rough or crepe-like character of the materialin Fig.

6, but Fig. 7 shows a small portion of one thin part of the diaphragm wall, with the crinkly or crepe-like surface formations of the layers somewhat exaggerated for explanatory purposes. The various layers or 1amin are secured together by any suitable c ement, but preferably I employ a cement in which tapioca is a principal ingredient, because this material contracts in drying, thus practically putting the entire diaphragm unterspaced relation; or, as shown in Fig. 3,

each laminationmay consist of a plurality of segments 11 with their edges abutting or overlapping' and these segment joints or seams in the different layers may be in interspaced relation.

The entire diaphragm comprises a plurality of zones of different thickness. In the particular example given there are four of these circular zones of which the inner or upper zone 12 and the outer intermediate zone 13 are of the minimum thickness consisting of the three layers or laminae above referred to, while the intermediate zone 14 and the peripheral zone 15 are of increased thickness, each consisting, -as shown, of six layers or lamin'produced in the case of zone 14 by cementing together and between certain of the main layers 10, strips or segments 162 Fig. 4; and in the case of the zone 15 the thlckening is obtained by the use of narrower strips or segments 17, Fig. 5.

While the width of these thickened zones and their location with respect to the diaphragm as a whole may be varied substantially, Fig. 6 shows preferred approximate of moderate width and located directly at the open marginV of the cone, while zone 14 is wider and located relatively near but spaced from they peripheral zone, so that the upper thin portion 10 is of a width approximately one-half the surface width of the cone; stiifened zone ,14 is wider, approximately one-third of the entire face width, and zones 13 and 15 are narrower'than the others. y l

In some cases vibrations of the outer thin zone 13 are additionally damped by a cord 18 encircling the diaphragm near the inner edge of the outervthickened zone 15,' and cemented in position as by the tapioca paste plateor board 20 forming -a part of the reproducing apparatus-as a whole or of its cabinet, by annular leather strips 21 and 22,

of which portions are cemented to the outer zone of the dia hragm at opposite sides thereof, and the ot er portions are cemented or otherwise secured tofether and to the front board or bafile board 20, thus providing a definite but iexible support for the periphery of the diaphragm, without im airmeiit of freedom and accuracy of its vi irations.

The form of the center, or a x, of the diaphragm may vary. Thus, in igs. 1 and 2 the central portion 24 may be flattened and suitable fittings may be secured to it for the connection of a drivin pin of any suitable audio amplifier, as wel understood in the art; or as shown in Fig. 6, the central portion may be cut away 'leaving an aperture 25 1n which one en-d o a sleeve 2G is inserted and secured by cementing. This sleeve may have an actuating coil, usually called a voice coil, of an audio-amplifier of the dynamic type, wound directly on it. l

In operation, the inward thin zone 10 of large area being located nearest the apex of the cone, and of relatively small diameter, has a natural vibration frequency corres ondin approximately to the audio-vibra tions o the higher frequenc ranges and these high notes are relative y emphasized by the thinness of the diaphragm; the intermediate thickened zone 14 is of dimensions which make it naturally responsive to vibrations of intermediate frequencies but the thickened structure of this zone also has a substantial damping effect reveiitin excessive relative loudness o sounds in this range and also tends to practically suppress the unwanted sixth harmonic. 'lhe marginal thickened zone 15 is of dimensions to res ond naturally to thelowest notes in thc au ible register and also by reason of its thickness sufiiciently damps these notes so that rattling or blasting are prevented and faithful reproduction is obtained.

The diaphragm as a whole therefore, irovides exce tionally faithful tone repro( uction with arge volume or acoustic pressure in proportion to energy applied to it by the driving pin o`r thelike, and it has been demonstrated in practice that the diaphragm gives im roved and satisfactory reproduction of't e entire audible range including very high and very low notes which are ordinarily cut off by diaphragins or other acoustic reproducers heretofore employed.

Preferably, the mass of the diaphragm in general, and-of theconstituent parts individually, is selected as low as possible, consistent with the desired relative rigidity of structure, the quality of reproduction and permanence of performance, whereby more faithful reproduction of the desirable high frequencies is attained. Also, the voice coil, see 27, Fi 6, is formed of lowest mass, and the metalic wire may be of aluminum or suitable alloy thereof, and likewise the mass the spirit of the invention.

of its spool is reduced to a minimum, to facilitate the reproduction of the desired high frequencies, in combination with the structure of the diaphragm proper.

Whereas, I have illustrated my invention by specific embodiments thereof, it will be understood that many changes and modifications inay be made without departing from l claim:

l. An acoustic diaphragm composed of a plurality of layers of soft, rough paper, secured together by cement.

2. An acoustic diaphragm composed of a plurality of layers of soft, rough paper,

'secured together by contractile cement.

3. An acoustic diaphragm composed of a plurality of layers of soft, rough paper, secured together by tapioca cement.

4. An acoustic diaphragm composed of a plurality of layers of crepe-like material connected by cement and having a plurality of annular zones of greater. thicknesses, toward the periphery.

5. An acoustic diaphragm composed of a plurality of layers of fibrous material connected by cement and having a )lurality of annular zones of different thicknesses, the thickened zones including additional lamin of the saine material.

An acoustic diaphragm composed of a plurality of layers of fibrous material connected by cement and having a plurality of annular zones of different thicknesses, and a cord-like damping element cemented to the diaphragm relatively near its periphery.

7. An acoustic diaphragm composed of a plurality of layers of ibrous material connected by cement and havinga plurality of annular zones of different thicknesses, and a cord-like damping element cemented to the dia )hragm relatively near its periphery and a( jacent the inner edge of an outer thickened zone.

8. An acoustic. diaphragm of fibrous material of moderate average thickness end including thickened annular zones, one located at the periphery and the other located at an intermediate position, of substantial width and spaced from the peripheral thickened zone.

9. An acoustic diaphragm of fibrous material of moderate. average thickness and including thickened annular zones, one located at the periphery and the other located at an intermediate position, of substantial width and spaced from the peripheral thickened zone and also in a location, relative to the axial dimension of the diaphragm, which is relatively near the outer peripheral zone and away from the apex of the diaphragm, leaving a relatively Wide zone of minimum thickness extending from the apex to said intermediate thickened zone.

Y10. An acoustic diaphragm composed of a plurality of layers of soft, rough paper, secured together by cement, peripheral strips of exible material secured to the peripher of the diaphragm and projecting lateral y for connection to a sound board or other support about an opening thereof. Y

11. A11 acoustic diaphragm of fibrous material of moderate average thickness and including thickened annular zones, one located at=the periphery and the other located at an `intermediate position, of substantial width andspaced from the peripheral thickened zone, peripheral strips of eXible material secured to the periphery of the diaphragm and projectingA laterally for connection to a sound board or other support about an optning thereof.

12. An acoustic diaphragm com osed of a plurality of layers of soft crepe ike paper secured together by contractile cement.

In testimony whereof Ihave signed this specification this 4th day of October 1930.

CHARLES FfDILKS. 

